1. Field of the Invention
The present invention relates to a reflection type photocathode and a photomultipler using the same.
2. Description of the Prior Art
The photomultiplier is a very versatile and sensitive detector of radiant energy in the ultraviolet, visible, and near infrared regions of the electromagnetic spectrum. In the photomultiplier, the basic radiation sensor is the photocathode which is located inside a vacuum envelope. Photoelectrons are emitted and directed by an appropriate electric field to an electrode or dynode within the envelope. A number of secondary electrons are emitted at the dynode for each impinging primary photoelectron. These secondary electrons in turn are directed to a second dynode and so on until a satisfactory gain is achieved. The electrons from the last dynode are collected by an anode which provides the signal current that is read out.
One type of the photomultipliers uses a reflection type photocathode and another type thereof uses a transmission type photocathode. The reflection type photocathode is typically made up of a nickel substrate, an aluminum layer deposited over the substrate, a layer of antimony and alkaline metal such as cesium (Cs), natrium (Na) deposited over the aluminum layer.
Various properties of the reflection type photocathode changes considerably depending on how the layer structure is determined or what kind of materials is used for each layer.